High-speed 2D measurement of edge turbulence phenomena with a fast camera in Heliotron J

Using gas puff imaging technique (GPI) the filamentary structure in edge plasma was firstly observed in Heliotron J. A combination of GPI and simultaneous movable Langmuir probe measurement shows that filamentary structure identified the turbulent burst in edge plasma, which was reported already in Heliotron J. In low electron density (<1 × 1019 m−3) the filamentary structure moves very fast, and its direction is the same as the Er × B drift. On the other hand, in high electron density (>2 × 1019 m−3) the motion of the filamentary structure is relatively slow, and typical lifetime of the filamentary structure is about 300–900 μs.